Neoseiulus (=Amblyseius) fallacis
This predaceous mite has a strong preference for pest mite species and will travel from tree to tree searching for them. It is found across the continental United States.
Adults are pear-shaped and slightly smaller than the European red mite adult. They are white until they feed when they take on the coloration of their prey (usually red or brown). The eggs are pear shaped, almost transparent, but slightly larger than the round European red mite eggs. The larvae are also transparent and difficult to see without a microscope.
Of the five N. fallacis life stages, only the larvae are six legged. All other post-egg stages have eight legs. In all stages, N. fallacis is indistinguishable from Galendromus pyri and G. occidentalis, other phytoseiid predatory mites, without a compound microscope.
Many; this page deals only with fruit trees.
In North American orchards, Neoseiulus fallacis strongly prefers tetranychid mites--the European red mite and the two-spotted spider mite--and will actively seek these.
Mated adult females overwinter in crevices of the tree bark if prey are available in the fall. They emerge as early as bloom, but in reduced numbers due to heavy winter mortality. N. fallacis increases in number rapidly and adults become numerous by July or August. They live about 20 days and lay an average of 40-60 eggs. Eggs are laid along the ribs of the undersides of leaves. Four to six generations are completed in a season in New York state. N. fallacis moves vigorously over plant surfaces in search of prey.
Because N. fallacis is a voracious consumer of mites and because its population increases quickly in relation to its prey, it can overtake an expanding pest population. It develops into the adult stage in about one third the time required by G. pyri. However, when N. fallacis has reduced the prey population, it will leave the tree in search of more tetranychid mites whereas G. pyri thrives on alternate foods. Over the winter, N. fallacis has a higher mortality rate than G. pyri. Therefore, a mixed population of N. fallacis and G. pyri is desirable.
Predatory mites are susceptible to many of the chemicals used to combat herbaceous mite infestations. A single application of a chemical considered highly toxic to N. fallacis at any time during the season will have a large negative impact on its abundance.
The habit of N. fallacis to overwinter in crevices can be used to advantage in the early spring with a pre-bloom horticultural oil application. This greatly reduces the number of European red mite eggs while not affecting predatory mite populations.
Pest mite problems are most common where pesticides are heavily used because predatory mite populations are killed along with target species It may take up to three years to establish a population of predators high enough to control pest mites. Integrated pest management strategies, as outlined in the tutorial of this guide, can help establish colonies of predatory mites.
N. fallacis is readily available from commercial suppliers (see the off-site publication, Suppliers of Beneficial Organisms in North America, page of the California Department of Pesticide Regulation website).
Thanks to Jan Nyrop for reviewing an earlier version of this section.
Kain, D. and Nyrop, J. March 1995. Predatory Mites. Insect Identification Fact Sheet No. 23. Cooperative Extension, Cornell University, Ithaca, NY.
Helle, W. and Sabelis, M.W. (Eds.) (1985) Spider mites: Their Biology, Natural Enemies and Control. Vol. 1B. Elsevier, Amsterdam. 458 pp.